Lead delays puberty. (Environment).

In children, even trace residues of lead can wreak harm. One recent study reported evidence of IQ deficits in children with blood concentrations of the metal below 5 micrograms per deciliter ([micro]g/dl) (SN: 4/26/03, p. 269), an amount found in 90 percent of U.S. kids. Now, epidemiologists have turned up evidence that similarly low lead concentrations delay puberty in girls.

Tiejian Wu of East Tennessee State University in Johnson City and his colleagues correlated signs of puberty in a nationally representative sample of 1,700 girls, ages 8 to 16, with the kids' blood-lead concentrations. The data came from a federal health and nutrition survey of the U.S. population.

Wu's group divided girls at each age into three groups on the basis of blood-lead concentrations: under 2 [micro]g/dl, at least 5 [micro]g/dl, or somewhere between those values. Among 10-year-olds, the share with pubic hair was 60 percent in the group with the lowest lead levels, 51 percent in the middle group, and just 44 percent in those whose blood concentrations were 5 [micro]g/dl or higher. By age 12, 68 percent in the lowest group had reached menarche compared with 38.5 percent in the group with the highest blood-lead concentrations. No firm link between blood lead and breast development emerged.

Wu says his team is now looking for evidence of a similar lead-linked slowing of reproductive maturation in boys.

The new findings, reported in the May Environmental Health Perspectives, are consistent with earlier animal data. Wu says they suggest that children can suffer significant development impacts at lead concentrations well below 10 [micro]g/dl--the threshold for what's deemed "elevated" by the federal government.--J.R.